There are some specific "Combo charts" available in the Chart Editor. From the help page:
A combo chart combines and displays the data from both a column chart and a line chart. A combo chart has either a single y axis (vertical), or two y-axes. The two data sets share the same x axis (horizontal).
You can specify the chart type and subtype for a report definition report by using the Chart Editor.
Other than these, I know of no way to combine arbitrary chart types.
Choosing "No limit" for the "Limit to top" value is the only auto-adjust setting. Otherwise, your only choices are 1-20 in the drop down.
The slider controls whatever group-by property you have put on the chart. It is basically used to focus in on a particular section of the chart (e.g., a certain subset of columns or bars).